After the famines, obesity is the next risk for millions

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To most people, sub-Saharan Africa is a region plagued by war, famine and disease. But it now faces a new threat - obesity.

It is not a problem widely associated with a continent where millions live on less than a dollar a day. But growing rates of obesity are threatening the health of the next generation.

With a population that has passed one billion, Africa is starting to experience the ills of the developed world, driven by changing diets, urbanisation and increasingly sedentary lives, according to research published in the British medical journal the Lancet.

The reasons for the steep rise in obesity among some of the world's poorest nations is hotly debated. One theory is that it is a legacy of evolution. People from Africa, Asia and Polynesia are particularly prone to obesity because they are more likely to have inherited the genes that encourage fat storage.

This is the "thrifty gene hypothesis" - the notion that obesity occurs especially among populations exposed in the past to alternating feast and famine. Months of food shortages and near starvation would be followed by weeks of feasting when the rains came.

Genes that laid down fat as a reserve against the next shortage were favoured - but among today's urban populations, for whom shortage never comes, the genes overdo their job.

In America, one adult in three is classified as obese, but obesity is markedly higher among black and native Americans than among those of European descent.

However, efforts to identify genetic reasons have failed, undermining the theory. As Nobel prize-winning biologist Sidney Brenner once said, the gene for obesity was found long ago - it is the one that makes you open your mouth.

The real culprit, researchers believe, is the shift to urban living. Cities in Africa are the fastest-growing in the world. This is not only about the spread of McDonald's, KFC and the "Coca-Colanisation" of the developing world. It is also about the move from growing to buying food.

The chief author of the Lancet study, Jenny Cresswell, said: "Once people move to the city, their activity levels go down. They are no longer able to grow their own food. Instead they tend to rely on street hawkers and eat foods high in fat and sugar.

"Today, obesity in Africa is associated with wealth; the wealthier you are, the more likely you are to be overweight. But as populations get richer, it is expected that the picture will swing round and obesity will become associated with the poor."

Researchers from the London School of Hygiene and Tropical Medicine, who analysed data from 27 countries in sub-Saharan Africa, say the increase in maternal obesity is threatening the lives of newborns.

The region has the world's highest neonatal death rate - deaths within four weeks of birth - and rocketing rates of obesity are driving it higher.

The researchers say babies of obese mothers have a 50 per cent higher risk of dying in the first month of their life.